interface Point2D {
  x: number
  y: number
}

// 接口可以通过 extends 继承
interface Point3D extends Point2D {
  z: number
}

const o1: Point2D = {
  x: 88,
  y: 77,
}

const o2: Point3D = {
  x: 88,
  y: 77,
  z: 99,
}
